Regulation device for a centrifugal separator to control discharge from outlets

ABSTRACT

In a centrifugal rotor ( 1 ) for separation of a substance from a liquid mixture supplied to the centrifugal rotor there is delimited a separation chamber ( 7 ) having peripheral outlets ( 30 ). The centrifugal rotor includes an outlet device ( 20-28 ) for intermittent opening and closing of the outlets ( 30 ) during rotation of the centrifugal rotor. An actuation device ( 31-40 ) may cause the outlet device ( 20-28 ) to keep the outlets ( 30 ) open to a varying extent and/or during a varying time, and a control device ( 43 ) is adapted to control the actuation device ( 31-40 ) in response to a sensed value of the amount of mixture supplied to the rotor, such that a predetermined amount of separated substance ( 29 ) having collected in the separation chamber ( 7 ) is discharged through the outlets ( 30 ) each time these are opened and closed.

FIELD OF THE INVENTION

The present invention relates to a centrifugal separator comprising arotatable centrifugal rotor, which delimits a separation chamber havingperipheral outlets for a separated substance, a stationary inlet devicefor introducing into the centrifugal rotor a liquid mixture thatcontains said substance and that is to be treated in the separationchamber, an outlet device which is rotatable with the centrifugal rotorand adapted to open and close said peripheral outlets intermittentlyduring rotation of the centrifugal rotor for discharging said separatedsubstance from the separation chamber and an actuation device arrangedoutside the centrifugal rotor and adapted to actuate said outlet deviceso that it maintains the peripheral outlets open to an extent and/orduring a time such that a predetermined amount of said separatedsubstance leaves the centrifugal rotor, said extent and/or time beingvariable. Particularly, the invention concerns a control device forkeeping constant the said amount of separated substance leaving theseparation chamber each time said peripheral outlets are opened andclosed.

BACKGROUND OF THE INVENTION

It is long known to use in connection with a centrifugal separator ofthe above defined kind sensing means by which it may be determinedexactly when a certain amount of said separated substance has beenaccumulated in the centrifugal rotor separation chamber and, then, toopen and close automatically said peripheral outlets. However, it hasproven difficult during a separating operation to accomplish dischargeof like amounts of such separated substance through the peripheraloutlets each time these are opened and closed.

The reason for this difficulty seems to be that a centrifugal rotor ofthe kind here in question has a poor ability of maintaining theperipheral outlets open to the same extent and/or during the same timeat each discharge operation and, therefore, to discharge alike amountsof substance at the various opening times. Thus, if a relatively smallamount of substance is discharged, the substance if it is constituted bysolid particles is given time to get a too high concentration of suchparticles before it is discharged through the peripheral outlets. Thiscan lead to the effect that part of the separated substance is giventime to fasten onto the inside of the walls of the centrifugal rotorbefore the peripheral outlets are opened. If, on the other hand, arelatively large amount of substance is discharged, the substance gets atoo low concentration of particles, i.e. the discharged substancecontains an undesired amount of the liquid from which the particlesshould be separated. This can lead to undesired losses, since it isoften the liquid that is the valuable part of the mixture being suppliedto the centrifugal rotor.

Even in separation cases where prior to a sludge discharge operation avaluable separated liquid is displaced radially inwardly in theseparation chamber, by supply to the separation chamber of a certainamount of a less valuable liquid having a higher density than thevaluable liquid, it may be of value that a well controlled amount ofseparated substance (particles and/or liquid) is discharged through theperipheral outlets each time these are opened and closed. Thus, itbecomes possible to optimize the amount of added less valuable liquidbefore every time the peripheral outlets are to be opened. The supply ofunnecessarily much liquid of this kind takes an undesired time intoaccount during which the separating operation is interrupted.

For resolving the above discussed problem to discharge a predeterminedamount of separated substance through the peripheral outlets, each timethese are opened and closed, design improvements have been constantlymade of said outlet device of the rotor and of the actuation devicesituated outside the centrifugal rotor for actuation of the outletdevice. However, this has not completely resolved the problem.Previously known devices for accomplishing a desired discharge ofseparated substance from a centrifugal rotor of the kind here inquestion is described for instance in U.S. Pat. No. 4,510,052 and WO97/27 945.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a control device bymeans of which the amount of separated substance leaving the separationchamber in a centrifugal rotor of the kind initially defined can be keptsubstantially unchanged every time the outlet device opens and closesthe peripheral outlets.

This object can be fulfilled according to the invention by means of aregulation device that is characterized by a sensing device for sensingof a parameter representative for the amount of mixture supplied perunit of time into the centrifugal rotor through said inlet device, and acontrol device which is connected both to the sensing device and to saidactuation device, the control device being adapted to receive from thesensing device a signal reflecting the amount of mixture, which per unitof time is supplied into the centrifugal rotor, and in response to saidsignal to control the actuation device—in accordance with apredetermined relation between the amount of mixture supplied per unitof time into the centrifugal rotor through the inlet device and theextent and/or the time that the peripheral outlets are to be maintainedopen by means of the outlet device—such that said predetermined amountof the separated substance leaves the centrifugal rotor. The saidrelation in certain cases may be calculated but in other cases has to bedetermined empirically.

Conventionally, in connection with a centrifugal separator of the kindhere in question, the said outlet device is adapted to actuate one ormore valves or slides of the centrifugal rotor by means of afluid—liquid or pressurized air—supplied to the centrifugal rotor bymeans of said actuation device outside the centrifugal rotor. An outletdevice of this kind may be used with advantage even in connection withthe present invention. However, within the scope of the invention, evenelectrically, magnetically, thermally or otherwise actuatable outletdevices may be useful.

Upon use of an outlet device that is actuatable by means of a suppliedfluid this outlet device may be of various kinds. Thus, the outletdevice may be adapted to open said peripheral outlets and keep theseopen to a varying extent or during a varying time depending upon thepressure by which said fluid is supplied by means of the actuationdevice. Alternatively, the outlet device may be adapted to operate independence of the amount of fluid or the amount of fluid per unit oftime delivered by the actuation device.

Even the actuation device may be of most varying kinds. In a case wheresaid fluid is a liquid and such liquid is to be supplied to the outletdevice at a variable but predetermined pressure, the actuation devicemay include a container for the liquid and a movable body, e.g. apiston, within the container for displacement of the liquid out of thecontainer. Further, the actuation device may include a container forpressurized air, possibly formed by part of the container for liquid.

The above said sensing device may be constituted by a conventional massor volume flow meter or by any suitable kind of equipment which directlyor indirectly is able to sense the magnitude of a liquid flow throughthe inlet device of the centrifugal separator, e.g. a pressure meter.The sensing device should be adapted to emit a signal of any suitablekind that is representative for the magnitude of the sensed liquid flow.The signal may have the form of an electric current or voltage, themagnitude of which is dependent on the magnitude of the sensed liquidflow.

The control device which shall receive the signal generated by thesensing device should be adapted in one way or another to control theaforementioned actuation device. The way in which such a control isaccomplished is, of course, dependent on the type of actuation devicehaving been chosen.

In a very simple case the actuation device may be adapted to supplythrough a conduit a so called operating liquid having a certainpressure. Then, a closing valve may be present in said conduit, whichvalve may be opened and be kept open during a certain controllableperiod of time. By means of an actuation device of this kind a desiredamount of liquid may be supplied to the centrifugal rotor during adesired period of time. Whereas the opening movement of said valve maybe initiated by an equipment adapted to determine the point of time whenthe peripheral outlets of the centrifugal rotor are to be opened, thetime for keeping the valve open may be controlled by said control devicein dependence of the signal from the sensing device.

In another case, which is described in detail below with reference tothe accompanying drawings, the actuation device may be adapted todeliver a liquid flow by means of pressurized air, the pressure of whichis variable. Thus, the magnitude of said air pressure may be controlledby means of the control device in dependence of the signal from thesensing device, the actuation device further being adapted to supplyonly a certain amount of so called operating liquid during a time thatis dependent on the chosen air pressure.

Other possibilities are described in the aforementioned patentspecifications U.S. Pat. No. 4,510,052 and WO 97/27 945.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described more in detail below with reference tothe accompanying drawing, in which FIG. 1 schematically shows part of acentrifugal rotor in section and various components included in aregulation device according to the invention. FIG. 2 shows more indetail an actuation device included in the regulation device.

DETAILED DESCRIPTION

FIG. 1 shows a part of a centrifugal rotor 1 that is rotatable around acenter axis 2 and that comprises an upper part 3 and a lower part 4. Therotor parts 3 and 4 are connected with each other by means of a lockring 5. Within the rotor there is arranged an annular slide 6 which isaxially movable a short distance to and from abutment against a lowerannular edge portion of the upper rotor part 3 under radial sealingagainst the lower rotor part 4 centrally within the rotor as well as atthe surrounding portion of the rotor.

Within the rotor a separation chamber 7 is delimited between the upperrotor part 3 and the slide 6, in which there is arranged a stack offrustoconical separation discs 8 coaxial with the rotor.

The stack of separation discs rests on a lower part of a so calleddistributor 9, which in turn rests on a conical partition 10 supportedby a central portion 11 of the lower rotor part 4.

The distributor 9, which has an annular cross-section, surrounds aninlet chamber 12 into which there extends a stationary inlet pipe 13 fora liquid mixture to be treated in the rotor. The inlet chamber 12communicates with the separation chamber 7 through several channelsdistributed around the rotor center axis 2 and delimited between theconical partition 10 and said portion of the distributor 9. Thepartition 10 carries on its upper side radially and axially extendingwings 14 between which said channels extend.

The inlet pipe 13 supports above the distributor 9 a so called paringdisc 15 adapted for discharge of liquid out of the rotor. The paringdisc 15 extends from the inlet pipe 13 radially out into an outletchamber 15 a. Between the outlet chamber 15 a and the separation chamber7 the upper rotor part 3 carries on its inside an annular partition 16,the inner edge of which forms an overflow outlet for liquid from theseparation chamber 7 to the outlet chamber 15 a.

Between the lower rotor part 4 and the annular slide 6 there is formed aso called closing chamber 17. This has a constantly open inlet 18 foroperating liquid close to the rotor center and closeable outlets 19 forsuch liquid in the vicinity of the rotor periphery. When the outlets 19are closed and the closing chamber 17 is filled with operating liquid,the slide 6 is kept in its upper position as can be seen from FIG. 1, inwhich it abuts axially against the edge portion of the upper rotor part3.

The rotor 1 supports on its underside an annular slide 20, which isaxially movable relative to the rotor in a way such that part of theslide 20 may close alternatively uncover the outlets 19 from the closingchamber 17. The slide 20 is pressed axially against the underside of therotor by several springs 21, which are distributed around the rotorcenter axis and which are supported by a support device 22. The supportdevice 22 is firmly connected with the lower part 4 of the rotor.Between the slide 20 and the rotor part 4 there is delimited an annularso called opening chamber 23, which has at least one central inlet 24and at least one outlet 25 at its radially outermost part.

The support device 22 supports an annular member 26, which forms aradially inwardly open first annular groove 27 that communicates withthe inlet 18 of the closing chamber 17. The member 26 also forms asecond such groove 28, which communicates with the inlet 24 of theopening chamber 23. The second groove 28 is situated at a level radiallyinside the first groove 27.

The above described details 20-28 and the annular slide 6 constitutetogether an outlet device rotatable together with the centrifugal rotorfor the discharge of a separated substance 29 from the separationchamber 7, when the slide 6 leaves its abutment against the upper rotorpart 3. Outside the annular slot which is then formed the lower rotorpart 4 has several ports 30 evenly distributed along the rotorperiphery.

Below the centrifugal rotor 1 there is arranged an actuation device foractuation of the just mentioned outlet device in a desired manner. Thisactuation device comprises a pressure tank 31 for pressurized air and aliquid supply device 32 arranged for supply of so called operatingliquid to the centrifugal rotor. A liquid supply pipe 33 leads from thedevice 32 into the groove 27 and communicates through a conduit 34 witha source of operating liquid. The conduit 34 has a check valve 35.

In a conduit 36, which connects the pressure tank 31 with the device 32,there is arranged a three-way valve 37.

The pressure tank 31 also communicates with a supply conduit 38 forpressurized air. This supply conduit 38 starts from a current/pressureconverter 39, which in turn through a conduit 40 communicates with apressurized air source (not shown).

The three-way valve 37 and the current/pressure converter 39 areconnected through signal lines 41 and 42, respectively, with a controlunit 43. This is also connected through signal lines 44 and 45 with aflow meter 46, e.g. mass flow or a volume flow meter, which is arrangedin an inlet device (not shown) through which the centrifugal rotor canbe charged with a liquid mixture, and with a sensing device 47,respectively, which is arranged in a n outlet conduit through which aliquid separated in the centriftugal rotor may leave this. The functionof the sensing device 47 will be described later.

FIG. 2 shows the liquid supply device 32 more in detail. FIG. 2 alsoshows the supply conduit 36 for pressurized air, the three-way valve 37therein, a part of the supply pipe 33 for operating liquid, the conduit34 and the check valve 35.

The liquid supply device 32 includes a cylindrical container 48 havingend walls 49 and 50. Within the container 48 a piston 51 is axiallymovable between two end positions under sealing against the surroundingwall of the container. In FIG. 2 the piston 51 is situated between itsend positions. The piston 51 divides the interior of the container 48 ina first chamber 52 and a second chamber 53.

On its one side the piston 51 is connected with a central piston rod 54,which in the shown position of the piston extends through an opening inthe end wall 50 and into the pipe 33.

The piston rod 54 has a central channel 55, which at one of its endsopens at the free end of the piston rod and at its other end—through aradially extending channel part—opens into the chamber 53.

While the chamber 52 through a hole in the end wall 49 constantlycommunicates with the supply conduit 36 for pressurized air, the chamber53 constantly communicates with the interior of the supply pipe 33 foroperating liquid; either directly through said opening in the end wall50, when the piston 51 is situated in the left half of the container 48,or through the channel 55 in the piston rod 54, when the piston 51 issituated in the right half of the container 48.

The centrifugal separator in the FIGS. 1 and 2 operates in the followingmanner.

After the centrifugal rotor 1 has been caused to rotate around thecenter axis 2 it is charged through the flow meter 46 and the inlet pipe13 a liquid containing a substance dispersed therein in the form ofsmall solids, which has a higher density than the liquid. The suppliedliquid mixture is conducted through the inlet chamber 12 and thechannels between the wings 14 into the separation chamber 7. When thisis full and liquid begins to be discharged from the rotor through theparing disc 15, free liquid surfaces are formed in the inlet chamber 12,the separation chamber 7 and the outlet chamber 15 a at the radiallevels shown by full lines provided with small triangles in FIG. 1.

During the rotation of the rotor the solids dispersed in the liquid areseparated by moving radially outwardly in the separation chamber 7. Theycollect in a layer 29 in the radially outermost part of the separationchamber, the so called sludge space. Liquid cleaned from particlesdischarges gradually through the overflow outlet formed by the partition16 and through the paring disc 15. After some time of separation theseparation chamber 7 has to be freed from the whole or part of theamount of particles having accumulated therein. This can take placeafter a predetermined time period of separation or when it has beensensed in one way or another that a certain amount of particles hasaccumulated in the separation chamber. FIG. 1 shows schematically asensing device 47 for this purpose. This sensing device is adapted tosense when the liquid discharging from the rotor starts to be turbid.Such a turbidity indicates that the separation going on is no longersufficiently effective, which in turn indicates that the interface layerbetween the accumulated particles and the cleaned liquid has reachedinto a certain radial level in the separation chamber. A signal aboutthis is sent from the sensing device 47 to the control unit 43, whichthen initiates a so called sludge discharge operation.

The equipment used for sensing that a certain amount of particles hascollected in the separation chamber may be of any desired suitable kind.Many different kinds of such equipment are previously known. It is notnecessary for the use of the present invention that a sensing equipmentof the kind here concerned is used at all.

Before a sludge discharge operation is initiated, the control unit 43has received a signal from the flow meter 46 through the signal line 44concerning the prevailing liquid flow into the inlet pipe 13. Thissignal has been converted to a weak electric current that through thesignal line 42 has been brought to actuate the current/pressureconverter 39. In dependence of the current strength the current/pressureconverter 39 has adapted the setting of a pressure reduction valve (notshown) in a way such that a relatively high pressure, e.g. 8 Bar,prevailing in the conduit 40, has been reduced to a somewhat lowerpressure, e.g. 5 Bar, which is maintained in the conduit 38 and thenalso in the pressure tank 31.

Depending upon which liquid flow that has been sensed by the flow meter46 the air pressure in the pressure tank 31 may be adjusted to a valuebetween for instance 3-6 Bar. An adjustment of this kind may beperformed either continuously depending upon occurring changes of thesensed liquid flow or discontinuously, e.g. at predetermined timeintervals or immediately before a sludge discharge operation is to beinitiated.

Upon initiation of a sludge discharge operation a signal is sent fromthe control unit 43 through the signal line 41 to the three-way valve37, which then is caused to open a previously closed connection betweenthe pressure tank 31 and the chamber 52 in the cylinder 48 (FIG. 2).

Hereby, the piston 51 which at this stage is situated at its endposition closest to the end wall 49 is caused to move rapidly to theright with respect to FIG. 2 and, then, to displace operating liquid(usually water) out of the chamber 53 through the pipe 33 to the annulargroove 27 in the rotor (FIG. 1).

It should be mentioned that the pipe 33 and the chamber 53 have beenkept completely filled with operating liquid through the conduit 34before said movement of the piston 51. This has been accomplished inthat a predetermined constant liquid pressure is maintained in theconduit 34, which liquid pressure ensures that the free cylindricalliquid surface in the groove 27 is maintained at a predetermined radiallevel indicated by a triangle in FIG. 1.

When the piston 51 pumps operating liquid from the chamber 53 out intothe pipe 33, this happens by a pressure which substantially exceeds thesaid predetermined constant pressure in the conduit 34. Thanks to thecheck valve 35 all this liquid will be conducted through the pipe 33into the groove 27 in the rotor. The liquid surface in the groove 27then will move radially inwardly, until liquid starts to flow over thelower limiting wall of the groove 27 and into the groove 28. From thegroove 28 the liquid is further conducted into the opening chamber 23,which is partly filled.

When a sufficient amount of liquid has entered the opening chamber 23for overwinning of the force from the springs 21, the slide 20 starts tomove downwardly, so that the outlets 19 of the closing chamber 17 areopened. However, already before the outlets 19 are opened, the liquidsurface in the opening chamber 23 will move to a level radially insidethe level, at which the slide 20 starts to move downwardly; this as aconsequence of the outflow through the outlet 25 from the openingchamber 23 being smaller than the inflow through the inlet 24 to theopening chamber 23. Thus, it is the flow speed of the liquid flowing inthrough the inlet 24 which decides how much liquid that is given time tobe supplied to the opening chamber 23.

When the slide 20 moves downwardly, operating liquid starts to leave theclosing chamber 17, the free liquid surface in the closing chamber 17 aswell as the free liquid surface in the groove 27 starting to moveradially outwardly. Then, the flow of operating liquid from the groove27 to the groove 28 will be interrupted, but thanks to the fact that theoutlet 25 from the opening chamber 23 is heavily throttled, so muchliquid is maintained during a certain period of time in the openingchamber 23 that the pressure force therefrom overwins the force of thesprings 21. The outlets 19 from the closing chamber 17 remain openduring this time.

When the liquid surface in the closing chamber 17 moves radiallyoutwardly, the axial force of the liquid in the closing chamber on theslide 6 is reduced, so that after a short period of time it becomessmaller than the counter directed force on the slide 6 from liquid andthe separated substance in the separation chamber 7. Hereby, the slide 6will be pressed axially downwardly and uncover the peripheral outletopenings 30 in the rotor part 4, so that separated substance starts tobe thrown out through these outlet openings.

At this stage so much operating liquid has left the opening chamber 23through the openings 25 that the force from the springs 21 can againbring the slide 20 axially upwardly to closing of the outlets 19 fromthe closing chamber 17.

This means that the movement radially outwardly of the liquid surface inthe closing chamber 17 is interrupted. As a consequence of new operatingliquid constantly being supplied to the groove 27 and the inlet 18, aswill be described later, the liquid surface in the closing chamber 17will not stop at a certain level, however, but instead begin to moveradially inwardly.

After a very short time the closing chamber 17 will contain so muchoperating liquid that the force therefrom on the slide 6 overwins thecounteracting force thereon from liquid and possibly remaining separatedsubstance in the separation chamber 7. Then the slide 6 again closes theperipheral outlets 30.

Before the piston 51 is moved to the left with reference to FIG. 2, thecontrol equipment 43 has adjusted the three-way valve 37 so that thechamber 52 is put into communication with the surrounding atmosphere.

The supply device 32 operates in the following manner.

When the three-way valve 37 is adjusted so that the pressure tank 31 isput into communication with the chamber 52, the piston 51 moves to theright under displacement of operating liquid from the chamber 53 outinto the pipe 33 and further to the groove 27 in the rotor. This happensrelatively rapidly until the piston rod 54 reaches up to and covers theopening in the end wall 50. Dependent upon the adjusted air pressure inthe pressure tank 31 it takes a longer or shorter time for the piston 51to move the just mentioned distance, which means that the set airpressure decided the flow speed (I/h) by which a predetermined amount ofoperating liquid is pumped into the groove 27 in the rotor.

This flow speed corresponds to the one by which operating liquid willflow from the groove 27 to the groove 28 and, thus, into the openingchamber 23. As mentioned earlier, this flow speed will be deciding forthe radially innermost level, at which a free liquid surface will besituated in the opening chamber 23, when the slide 20 is situated in itslower position, i.e. when the outlets 19 from the closing chamber 17 arekept open. The closer the rotor center axis this level in the openingchamber 23 is situated, the longer time it will take before the openingchamber 23 has been emptied of so much operating liquid that the springs21 return the slide 20 to closing of the outlets 19. This influences inits turn the amount of operating liquid which is given time to leave theclosing chamber 17 and, thus, the radially outermost level to which theliquid surface in the closing chamber 17 is allowed to move. Theposition of this level determined in its turn how much separatedsubstance that is allowed to leave the separation chamber 7, since themovement radially outwardly of the free liquid surface in the separationchamber will become dependent thereupon.

When the piston 51 has moved so far to the right in the cylinder 48 thatthe piston rod 54 covers the opening in the end wall 50, the liquidlevel in the groove 27 in the rotor has already started to move radiallyoutwardly.

More or less liquid (or no liquid at all) is then left in the groove 27.When the piston 51 continues its movement to the right, a flow comes upthrough the channel 55 in the piston 54 from the chamber 53 to andthrough the pipe 33. This flow is substantially smaller than the flowpreviously caused by the piston 51 but larger and more controlled thanthe flow which can come up through the conduit 34 to the pipe 33.

The flow now accomplished by means of the piston 51 into the groove 27and from there into the closing chamber 17 is to accomplish that theliquid surface in the closing chamber 17 moves radially inwardly fasterthan the corresponding movement of the free liquid surface in theseparation chamber 7. If this does not happen, the slide 6 will again bepressed downwardly, namely, and uncover the outlet openings 30. That theliquid surface in the separation chamber 7 moves inwardly depends on thefact that the supply of mixture through the inlet pipe 13 is notinterrupted during a sludge discharge operation.

When the piston 51 has reached its end position at the end wall 50, uponneed further operating liquid is supplied automatically through theconduit 34, until the liquid surface in the groove 27 has retained itspredetermined radial position, which corresponds to the aforementionedconstant liquid pressure in the pipe 33 prevailing in the conduit 34upstream of the check valve 35.

From what has been said it can be seen that setting of a lower or higherair pressure in the pressure tank 31 leads to a smaller or a larger,respectively, amount of separated substance leaving the separationchamber 7 during a sludge discharge operation.

As has been mentioned earlier, the present invention has for its objectto accomplish a constant amount of separated substance being removedfrom the separation chamber at each sludge discharge operation. It hasbeen proved that this can be obtained by actuation of the centrifugalrotor opening device for uncovering of the peripheral outlets 30 independence of the magnitude of the flow of liquid mixture being suppliedto the centrifugal rotor.

A possible explanation to this is that a certain flow of liquid mixtureinto the centrifugal rotor through the inlet pipe 13 gives the resultthat a free liquid surface is formed at a certain level in the inletchamber 12 (see the full line in FIG. 1), but that upon a larger flow afree liquid surface is formed at a level radially closer to thecentrifugal rotor center axis (see the dotted line in FIG. 1).

The reason for this would be that the flow resistance for the liquidflowing in the separation chamber 7 through the very thin separationpassages between the separation discs 8 increases by an increased flowthrough the centrifugal rotor.

Upon a changed liquid level in the inlet chamber 12, as just described,the force against the slide 6 from the liquid present in the separationchamber 7 will be changed, which influences the previously describedcourse as to the movement of the slide 6. Thus, the slide 6 upon anincreased liquid pressure in the separation chamber 7 will be subjectedto an enlarged opening force, which—if the conditions on the operatingliquid side of the slide 6 remain unchanged—leads to a prolonged openingtime for the outlets 30 during a sludge discharge operation.

By the invention such an increased liquid pressure in the separationchamber 7 as a consequence of an increased flow into the centrifugalrotor may be compensated in a way such that a somewhat lower airpressure is set in the pressure tank 31. The result of this is thatoperating liquid is supplied to the rotor by means of the supply device32 at a somewhat lower speed than normally, i.e. the opening chamber 23will be filled to a somewhat smaller degree and, therefore, be emptiedsomewhat faster than normally. The movement radially outwardly of thefree liquid surface in the closing chamber 17 thereby will beinterrupted somewhat earlier than normally, i.e. in a radial positionsomewhat closer to the rotor center axis than normally.

Hereby, it has been achieved an adaptation of the liquid pressure on theslide 6 from the operating liquid in the closing chamber 17 in relationto the changed liquid pressure on the slide 6 from the liquid in theseparation chamber 7.

A sensing device 46 has been described above as placed in connection tothe stationary inlet pipe 13 of the centrifugal rotor for sensing of aparameter that is representative for the amount of mixture which perunit of time is conducted into the centrifugal rotor. However, a sensingdevice for this purpose need not be situated in connection to thestationary inlet pipe 13 but can, alternatively, be placed within therotor or in a stationary outlet conduit from the rotor, wherethroughseparated liquid leaves the rotor.

If the sensing device is arranged within the rotor, it may have the formof a liquid level meter, i.e. a floating body, in one of the chambers ofthe rotor, e.g. the inlet chamber 12. Alternatively, it may have theform of a pressure meter.

What is claimed is:
 1. A regulation device for a centrifugal separator,which comprises a rotatable centrifugal rotor (1), which delimits aseparation chamber (7) having peripheral outlets (30) for a separatedsubstance, a stationary inlet device (13) for introducing into thecentrifugal rotor a liquid mixture, which contains said substance andwhich is to be treated in the separation chamber (7), an outlet device(20-28), which is rotatable together with the centrifugal rotor (1) andadapted intermittently to open and close said peripheral outlets (30)during rotation of the centrifugal rotor for discharge of said separatedsubstance from the separation chamber (7), and an actuation device(31-40) situated outside the centrifugal rotor (1) and adapted toactuate said outlet device (20-28) such that it maintains the peripheraloutlets (30) open to an extent and/or during a time such that apredetermined amount of said separated substance leaves the centrifugalrotor (1), said extent and/or time being variable, wherein a sensingdevice (46) for sensing of a parameter that is representative for theamount of mixture which per unit of time is supplied into thecentrifugal rotor (1) through said inlet device (13), and a controldevice (43), which is connected both to the sensing device (46) and tothe actuation device (31-40), the control device (43) being adapted toreceive from the sensing device (46) a signal reflecting the amount ofmixture, which per unit of time is supplied into the centrifugal rotor(1), and in response to said signal to control the actuation device(31-40)—in accordance with a predetermined relation between the amountof mixture supplied per unit of time into the centrifugal rotor (1)through the inlet device and the extent and/or time that the peripheraloutlets (30) are to be maintained open by means of the outlet device(20-28)—such that said predetermined amount of the separated substanceleaves the centrifugal rotor (1).
 2. A regulation device according toclaim 1, in which the sensing device (46) is constituted by a flow meterplaced in connection to said stationary inlet device (13).
 3. Aregulation device according to claim 2, in which the actuation device(31-40) is adapted to actuate the outlet device (20-28) by supply of anoperating liquid to the centrifugal rotor.
 4. A regulation deviceaccording to claim 3, which the actuation device (31-40) includes meansfor supplying a variable flow of operating liquid.
 5. A regulationdevice according to claim 4, in which said means for supplying includesa pressure tank (31) arranged to contain pressurized air and a container(48) arranged to contain said operating liquid, a movable wall in thecontainer (48), being arranged by actuation of the air pressure in thepressure tank (31) to displace said operating liquid out of thecontainer, and said control device (43) being arranged to control theair pressure in the pressure tank (31) in dependence of said signalreflecting the amount of mixture which per unit of time is supplied intothe centrifugal rotor (1).
 6. The regulation device according to claim5, in which said movable wall is a piston (51).
 7. A regulation deviceaccording to claim 1, in which the actuation device (31-40) is adaptedto actuate the outlet device (20-28) by supply of an operating liquid tothe centrifugal rotor.
 8. A regulation device according to claim 7, inwhich the actuation device (31-40) includes means for supplying avariable flow of operating liquid.
 9. A regulation device according toclaim 8, in which said means for supplying includes a pressure tank (31)arranged to contain pressurized air and a container (48) arranged tocontain said operating liquid, a movable wall in the container (48),being arranged by actuation of the air pressure in the pressure tank(31) to displace said operating liquid out of the container, and saidcontrol device (43) being arranged to control the air pressure in thepressure tank (31) in dependence of said signal reflecting the amount ofmixture which per unit of time is supplied into the centrifugal rotor(1).
 10. The regulation device according to claim 9, in which saidmovable wall is a piston (51).